1. Field of the Invention
This invention relates to a vibration wave driven actuator for effecting relative movement of a vibration member and a member being in contact therewith by a travelling vibration wave generated by the vibration member, and more particularly to a support device for supporting and fixing the vibration member relative to a fixed member without hampering vibration.
2. Related Background Art
Vibration wave motors utilizing a travelling vibration wave have recently been put into practical use and the epitome of the principle thereof is as follows.
A ring-like vibration member of resilient material whose full circumferential-length is as great as integer times a certain length .lambda. having two circumferentially arranged groups of piezo-electric elements (hereinafter referred to as the A piezo-electric element group and the B piezoelectric element group) secured to one surface thereof is used as a stator. These piezo-electric elements are arranged at a pitch of .lambda./2 and so as to be alternately opposite in constructiveness in the A and B groups, respectively, and are disposed so that there is deviation as great as odd number times .lambda./4 between the A and B groups. Electrode films are applied to the A and B groups of the piezo-electric elements. If an AC voltage is applied to only one of the two groups, for example, the A groups, there is generated in the vibration member over the full circumference thereof a standing wave (wavelength .lambda.) of outside--the surface vibration which is a flexural vibration in which the central point of each piezo-electric element of the A group and a point distant by .lambda./2 therefrom are the positions of antinode and the middle point between the positions of antinode is the position of node (hereinafter referred to as the standing wave A). If an AC voltage is applied to only the B group, there is likewise generated a standing wave (hereinafter referred to as the standing wave B), but the positions of the antinode and node thereof deviate by .lambda./4 relative to the standing wave A. If AC voltages of the same frequency and having a time phase difference of .pi./4 are applied to the A and B groups at a time, there is generated in the vibration member a travelling wave (wavelength .lambda.) of flexural vibration travelling in the circumferential direction, as a result of the combination of the standing waves of the two, and at this time, each point on the other surface of the vibration member having a thickness effects a kind of elliptical movement. Consequently, if a ring-like movable member as a rotor is brought into pressure contact with said other surface of the vibration member, the movable member is subjected to a circumferential frictional force from the vibration member and is rotatively driven. The direction of that rotation can be reversed by changing over the phase difference between the AC voltages applied to the A and B piezo-electric element groups to the positive or the negative. What has been described above is the epitome of the principle of the vibration wave motor of this kind.
On the other hand, as regards the supporting of the travelling vibration wave motor, it is difficult to fix the vibration member without spoiling vibration energy because in the vibration member, there is not a point which is not displaced at all, i.e., a node of vibration, and usually the vibration member is fixed to the fixed member with a flexible material such as a felt interposed therebetween.
Also, there has been proposed a structure in which as disclosed in U.S. Pat. No. 4,634,915, an auxiliary vibrator is provided on the vibration member to support the latter.
However, in the support structure using felt or the like as described above, accurate positioning of the vibration member is impossible and there is a disadvantage that the vibration insulating effect is deteriorated by a change with time, etc., and moreover, although the support against the pressure force of the rotor is possible, it is nearly impossible to support the reaction force of the driving force and therefore, another member as disclosed in Japanese Laid-Open Patent Application No. 62-213585 has been required for the reaction force of the driving force.
Also, in the support structure using the auxiliary vibrator as shown in U.S. Pat. No. 4,634,915, the fixed portion cannot be a completely fixed end and therefore, vibration is propagated to the fixed member or the vibration of the vibration member is disturbed and in addition, the auxiliary vibrator requires a predetermined length in a direction perpendicular to the direction of travel of the travelling wave of the vibration member, and this has led to the disadvantage that a large space is occupied and the volume of the entire motor becomes large.